New gazebo sensor

I followed the tutorial on adding new Gazebo assets to configure a new sensor, as well as the development guide for creating new Gazebo assets. In both, when trying to use a new sensor and the file model.sdf.jinja, you must add the following lines to quadrotor_base.sdf.jinja:

``{% elif sensor.model == 'rgbd_camera' and not sensor.gimbaled -%}``
`` {% include 'rgbd_camera/rgbd_camera.sdf.jinja' with context %}``

If you miss these lines, the model.sdf will be used by default.

IMPORTANT: If the new sensor must be on the gimbal, the model.sdf.jinja file must be used.